The invention relates to an apparatus for measuring the mass of a motor vehicle.
In order to determine the most favorable shift points for an automatic gearbox of a motor vehicle or to give the driver of a vehicle with manually shifted gear box optimum shift recommendations by means of an appropriate display device, the particular total mass of the vehicle must be known. However, with commercial vehicles in particular, the mass may vary in a wide range. It must be taken into account here that a trailer or semitrailer may also be included, the mass of which cannot be ignored. A loaded heavy truck train can, for example, be approximately five times heavier than the empty traction vehicle. In the Federal Republic of Germany for example, the total weights of typical heavy duty vehicles or trains lie between about 8 tons and about 38 tons.
In view of the wide range of possible vehicle weights, it is not possible to work with fixed given values for the mass of the vehicle in determining the shift points or shift recommendations.
Up until now, no suitable methods for determining the mass have yet been proposed.
The basically conceivable method of attaching dynamometers to the axles for example has the disadvantage that on truck trains dynamometers and wiring are also necessary on the trailer. An extremely high level of expenditure on technical equipment with correspondingly high costs would therefore have to be accepted. The same applies to position transducers with which the vehicle mass is determined via the jounce of the individual axles.
A less expensive method consists in detecting the acceleration and deceleration behavior of the vehicle in successive vehicle states with different drive torques and calculating the mass in a microcomputer using the equations of motion. The mass of a trailer which may be included is recorded here automatically. In this process, the accelerations acting on the vehicle may be determined, inter alia, from changes in the engine speed or wheel speed. The acting engine torque is, for example, taken from tables, which are electronically stored, as a function of engine speed and control rod displacement of the injection pump. A problem here is that inaccuracies must be expected due to individual variations and parameter changes, such as air pressure, temperature, etc.
Therefore, it is the object of the invention to create an apparatus which permits the mass of a vehicle or of a vehicle train to be determined at high accuracy within a large measuring range with little structural expenditure.
This object is achieved by measuring the speed of the engine and the instantaneous transmission ratio of the transmission line of the vehicle and using a computer, to store a series of consecutive engine speed values, calculate the period or frequency of periodic speed fluctuations using the stored engine speed values and generating a measured value signal for the mass of the vehicle as a function of the frequency of periodic speed fluctuations and of the transmission ratio.
Apart from the computer, which can if necessary also be used for other control functions within the vehicle, only sensors for the speed of the engine and the particular transmission ratio are required. According to a preferred embodiment, a speed transducer for the gearbox input speed and a vehicle velocity transducer (speedometer) or a transducer for the gearbox output speed are used. The transmission ratio can be readily calculated from the vehicle velocity and engine speed or from gearbox input and output speeds.
Instead of the vehicle velocity transducer, a transducer for the gear, engaged at the time, of the vehicle gearbox--for example switches cooperating with the shift lever or adjusting members of the gearbox--may be used.
As the oscillations in the transmission line occur more intensely with load changes, a particularly preferred embodiment of the invention provides for transducers reacting to load changes to be arranged and connected to an input of the computer, the computer executing a determination of the mass only after a load change. Such transducers may, for example, react to the actuation of the clutch, in particular to the clutch engagement, to movements of the accelerator linkage of the engine, for example adjusting rods of the injection pump, or else to gear changes of the gearbox.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.